This disclosure relates to semiconductor memory devices, more particularly those incorporating phase change memory cells, as well as memory systems including same and related methods of programming same.
Semiconductor memory devices may be classified as volatile and non-volatile in their operative nature. Volatile memory devices are typically configured to store data by charging/discharging capacitors in memory cells, and are widely used as main memories in a broad range of electronic devices. Volatile memory devices, such as Dynamic Random Access Memory (DRAM) and Static Random Access Memory (SRAM) are able to retain stored data only so long as power is supplied, but lose stored data in the absence of applied power.
In contrast, non-volatile memory devices, such as flash memory, are able to retain stored data in the absence of applied power. Thus, non-volatile memory devices are commonly used to store program code and/or data within computers, mobile devices, etc.
In response to memory devices characterized by high data storage capacity, fast operating speed, and low power consumption, new memory devices have been developed seeking to emulate the DRAM integration density, SRAM operating speed, and the non-volatile operating nature of flash memory all in a single memory device. These next generation memory devices include, for example, the Phase Change Random Access Memory (PRAM) that uses a phase change material to store data, the Resistance Random Access Memory (RRAM) which uses materials having a variable resistance such as transition-metal oxides to store data, and the Magnetic Random Access Memory (MRAM) which uses ferromagnetic materials to store data. The foregoing constituent materials all exhibit a similar characteristic in that their resistance varies in relation to the magnitude and/or direction of an applied voltage and/or current. Yet, once data is programmed using any one of these approaches, the corresponding resistance characteristic will not change when the application of power is interpreted, and no data refresh operation is required.
Each memory cell in these next generation resistive memory devices may be formed with a single resistive element and a corresponding switching element so that data may be stored by controlling the voltage and/or current applied to a bitline and a wordline to thereby change the resistive state of the resistive element.
Unfortunately, the time required to program data in many resistive memory devices, and particularly the PRAM device, is significantly longer than commonly used conventional memory devices. Accordingly, improvements are required to generally reduce the time required to program data in resistive memory devices and increase programming efficiency.